Typically, the sensitivity of emission spectrometry that uses emission phenomena of substances, molecules, or atoms is very high. Analyses in which samples are irradiated with light and light radiated from the samples is used are also in use. Absorptiometry and Laser Induced Fluorescence (LIF) are examples of such optical analyses.
In recent years, there is a demand that the size of the above-mentioned optical measurement devices and optical measurement apparatuses be reduced to a portable size. Also, there is a demand for an increased measurement performance.
The reduction in the size of an optical measurement apparatus leads to a reduced distance between a light source that irradiates a sample with light and a detector that monitors observation light from the sample within the apparatus. Optical elements, such as a condenser lens and an optical filter, are present in a light guide path constituting an irradiation optical system for guiding irradiation light from the light source to the sample or in a light guide path constituting an observation light collecting optical system for guiding observation light from the sample to the detector. Thus, an influence of stray light that can act as noise in the measurement, such as reflected light and scattered light, generated while light travels in a light guide path within the apparatus becomes more prominent as the size of the apparatus is reduced. Such stray light is also generated on an inner wall of the apparatus housing.
The inventors have proposed a light-induced fluorescent measurement device (Patent Literature Document 1) in which an optical system and a monolithic housing are built with resin that at least partially contains a pigment, in order to reduce the influence of stray light as much as possible and also to reduce the size of an optical measurement apparatus. This relates to an LIF apparatus.
Specifically, the light-induced fluorescent measurement device has the following characteristic configuration. (1) A light guide path of an irradiation optical system and a light guide path of an observation light collecting optical system are partially filled with resin transparent to irradiation light and observation light. (2) Another resin is provided to enclose the transparent resin of these light guide paths. This resin contains a pigment. (3) The pigment has a property of absorbing stray light. An amount of the pigment to be contained in the resin is set to an amount at which at least the stray light is entirely absorbed. (4) Resin materials in the transparent resin and in the pigment-containing resin are of the same type.
The above-described configuration provides the following advantageous effects, for example. As the resin materials in the transparent resin and in the pigment-containing resin are of the same type, reflection or scattering of light at an interface where the two resins are in contact with each other is suppressed. The stray light incident onto the pigment-containing resin is absorbed by the pigment. Therefore, almost no stray light returns to the transparent resin of the light guide paths. Furthermore, no stray light leaks to the outside of the pigment-containing resin. Therefore, almost no complex multiple reflection of stray light occurs. Consequently, no measure against the complex multiple reflection needs to be taken in the observation light collecting optical system.